1. Field of the Invention
The present invention relates to a maintenance-free stone tile in which an inorganic glassy coating layer excellent in high hardness and high mirror surface glossiness is formed on a surface of a stone that may be of various type, such as marble or granite, and any subsequent maintenance is not required; a coating agent therefor; and a method for producing the tile.
2. Description of the Related Art
Conventionally, the maintenance of floors of various stone, such as marble, an artificial stone and terrazzo, is generally done by a wax method or grinding with a diamond grindstone. The wax method has many problems from the viewpoint of quality, glossiness-maintaining performance etc., and has other problems, one thereof being a problem that it is indispensable to make a work of peeling the wax periodically and further a beautiful appearance of the floors is remarkably damaged by darkening and stains if the work is left undone. It is therefore difficult to keep the floors in a high quality state over a long term. Furthermore, a wax-peeling agent itself is strongly alkaline to decrease the glossiness of the stone and make the stone themselves brittle. Thus, the maintenance based on this method is a method not recommendable very much. In the meantime, according to the grinding with a diamond grindstone, a grinding work having about 5 to 7 steps is necessary for mirror-finishing the floors so that much labor is required to maintain and control the floors. Moreover, even when marble is ground with much labor, marble is decreased in glossiness after several months since marble itself is a soft stone. Accordingly, unless the stone is periodically ground, the material is not easily kept in a high quality state over a long term. Furthermore, water used for the grinding makes the stone itself brittle. Thus, the method is not very desirable for stones. In recent years, in order to solve these problems, various coating agents for stone have been proposed. However, even when these coating agents are adopted, there remain problems as described below.
(1) Damage in Mirror Surface Glossiness:
When a silicone-based coating agent, or a resin-based coating agent that may be of various types is applied to surface of marble, the surface generally gains a high glossiness but is damaged in mirror surface degree not to gain a high-quality finish. The reason why the mirror surface degree is damaged is generation of air bubbles, application unevenness or coating streaks on the application. Additionally, the stone itself absorbs the agent to damage the mirror surface degree to give a finish poorer in appearance than mirror surface finish obtained by grinding with a diamond grindstone.
(2) Unstable Adhesiveness:
A main component of marble, artificial stones, terrazzo and others is calcium carbonate. Thus, such stones are basically bad in adhesiveness to hard coating agents so that after the application of the agents, a poor adhesion of the agents may generate vertical injures, peels or others. Moreover, the resultant coating film shrinks by condensation reaction to be easily, for example, cracked or peeled. Thus, the stones are remarkably damaged in quality.
(3) Difficult Maintenance:
Even when a coating film can be formed, the film may be, for example, injured, peeled or cracked with time for the above-mentioned reasons. Thus, even the stone is re-coated, resulting in an uneven finish. Later repair often becomes difficult. Resin coating agents also become conspicuously darkened with time, so that in the same manner the stone turns into a state of not being easily repaired. In short, the existing covering-type coating agents have a problem of being gradually deteriorated in quality with the passage of time.
(4) High Slipperiness:
When a silicone-based or resin-based coating agent is applied, the slipperiness of the resultant floor surface generally becomes a problem in both a dry state (the floor surface is dry) and a wet state (the floor surface is wet) to increase a risk of a falling accident or other accidents. Silicone-based coating agents are generally high in water repellency to give a very high slipperiness in a wet state. In the meantime, resin-based coating agents are increased in slippage, which follows deterioration in the glossiness of the agents (surface roughness). Thus, whether floor surface is in a dry state or in a wet state, a falling accident or other accidents are easily caused.
Since there remain problems as described above, at present the maintenance of various stone in various commercial facilities, hotels, public facilities, play or game facilities, and others inside and outside Japan is generally a maintenance method using grinding, or maintenance using a wax method. Thus, maintenance-free stone tiles have not been provided.
An invention disclosed in Patent Literature 1 (Japanese Patent No. 4957926 (JP 2010-163584 A)) proposed previously is about a maintenance method for a vinyl chloride floor, using an inorganic coating layer. This Patent Literature 1 discloses “a flexibility-given and ambient-temperature-hardenable inorganic coating agent for protecting a chemical floor, in which at least a mixture of tetrafunctional and trifunctional alkoxysilanes, the proportion of the mixture being from 10 to 45% by weight of a composition of the whole of the coating agent, is mixed with colloidal silica superfine particles having an average particle size of 5 to 20 nm, the proportion of the particles being from 10 to 50% by weight of the composition; and further the following are blended into the composition to give flexibility to a coating layer for a soft vinyl chloride floor: a silicone alkoxy oligomer and/or a bifunctional alkoxysilane, the proportion of the component(s) being from 2 to 20% by weight of the composition; a silane coupling agent in which one or more functional groups of a vinyl group, an epoxy group and/or an amino group is/are used, as a binder for the colloidal silica superfine particles and the alkoxysilanes, the proportion of the agent being from 0.5 to 2.0% by weight of the composition; and, e.g., a phosphoric acid based catalyst and/or a titanium based catalyst, as one or more catalyst(s) for promoting a condensation reaction of silanols produced by the hydrolysis of the alkoxysilanes, the proportion of the catalyst(s) being from 0.5 to 5% by weight of the composition.
However, according to Patent Literature 1, in order that a coating agent can be caused to follow a soft and flexible chemical floor material such as vinyl chloride, and a layer of the agent can maintain a high-hardness top coating layer, it was necessary to introduce the silicone alkoxy oligomer and/or the bifunctional alkoxysilane for giving flexibility. However, in the present invention, a floor material itself is a hard stone; thus, the invention is characterized in that it is unnecessary to give flexibility as attained by a coating agent for chemical floors, consider recoating, and use an underlying material for heightening the coating agent of the present invention in adhesiveness to the substrate.
According to a vinyl chloride based tile subjected to a laminated-type inorganic protective coating processing, and a coating method therefor in WO/2014/129081, a laminated-type coating layer is formed on the surface of a vinyl chloride based tile, thereby making it possible to form a maintenance-free coating layer having a hardness corresponding to a pencil hardness of 10H or more, desirably 12H or more even when this tile is a soft vinyl chloride based tile. However, a coating agent for stone does not need to be made into a laminated-type coating layer for the purpose of stress relaxation since floor materials themselves of stones are very hard. A super hard top coating monolayer finish can produce a maintenance-free state.